The present invention relates to automatic guided vehicle (AGV) systems and, more particularly, to an AGV system having guided and unguided paths and in which communications data and vehicle guidance signals are transferred among AGVs and a communications and traffic controller.
In the field of material handling, most commonly in a warehouse environment, many articles must be stored in inventory and, an indefinite time later, retrieved for use. The larger the warehouse facility, the greater the number of objects that can be stored.
Moreover, large warehouse facilities require a great amount of geographical space. Not only are modern warehouses spread over an appreciable distance, but their height allows many objects to be stacked for storage one above the other. Each object location or bin can be identified along three axes: X, Y and Z. Thus, a warehouse location for any specified particular object can be uniquely identified.
When the warehouse is large, it becomes burdensome to move material from one part (e.g., the port of entry) to another part thereof (e.g., a storage bin). Moreover, certain warehouses house large objects, weighing many pounds or even tons. The combination of large objects to be stored in a warehouse and great distances between pickup and delivery (P & D) stands lends itself to assigning tasks to automatic guided vehicles. As used herein, the term "assignment" indicates an address of a P & D stand for a pickup or a delivery operation.
It has been found that guided vehicles moving over a buried inductive cable can perform many of the functions that humans perform without the requirements of lighting, heating, ventilation and air conditioning that would normally be mandatory for modern human working conditions. Moreover, AGVs can be relied upon to operate continuously 24 hours per day. These advantages of performance over human laborers result in greater efficiency for warehouse facilities.
In certain environments, it is impossible to provide a buried inductive cable at all locations over which an automatic guided vehicle is to travel. For example, it may be difficult or impossible to bury a cable between a plurality of buildings that form one warehouse facility. Other obstacles to burying cables may be metallic floors, nearly impermeable rock formations and the like.
When an AGV must travel over an unguided path (i.e., an area in which a buried cable is not present), prior systems have failed to control or even communicate with the AGVs, resulting, of course, in loss of overall system integrity.
For prior art systems in which communications and guidance information is constantly required, only closed loop systems with no interruption could be used, thus limiting an automated warehouse's usefulness.
Another general disadvantage of prior art systems is that, when they address the problem of communications at all, they create separate systems for communications with AGVs and for controlling traffic. It has been found that separate subsystems that communicate with AGVs and that manage or control traffic can cause unforeseen difficulties in overall warehouse management. For example, a communications signal that instructs an AGV to move in one direction may conflict directly with an instruction that would otherwise optimize traffic control. The result can be grid lock or other sorts of traffic jams and inefficiencies.